Solifluction rates, processes and landforms: a global review

Field data on the rates of solifluction and associated parameters are compi led from the literature, in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms, with special a ttention on the climate-solifluction. relationship. The analyzed data origi nate from 46 sites over a wide range of periglacial environments, from Anta rctic nunataks to tropical high mountains. Solifluction, broadly defined as slow mass wasting resulting from freeze-thaw action in fine-textured soils , involves several components: needle ice creep and diurnal frost creep ori ginating from diurnal freeze-thaw action; annual frost creep, gelifluction and plug-like flow originating from annual freeze-thaw action; and retrogra de movement caused by soil cohesion. The depth and thickness of ice lenses and freeze-thaw frequency are the major controls on the spatial variation i n solifluction processes. Near the warm margin of the solifluction-affected environment, diurnal freeze-thaw action induces shallow but relatively rap id movement of a superficial layer 5 - 10 cm thick on average, often creati ng the thin stone-banked lobes typically seen on tropical high mountains. I n addition to diurnal movement, annual frost creep and gelifluction may occ ur on slopes with soil climates of seasonal frost to warm permafrost, dislo cating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium-size solifluction lobes. In High-Arctic col d permafrost regions, two-sided freezing can induce plug-like flow of a soi l mass 60 cm or thicker. The correlation between process and landform. sugg ests that the riser height of lobes is indicative of the maximum depth of m ovement and prevailing freeze-thaw type. Climate change may result in new d ifferent ground freezing conditions, thereby influencing the surface veloci ty and maximum depth of soil movement. Soil moisture and topography also co ntrol solifluction. High moisture availability in the seasonal freezing per iod enhances diurnal freeze-thaw action and subsequent seasonal frost heavi ng. The latter contributes to raising the moisture content of the thawed la yer and promotes gelifluction during the thawing period. The slope angle de fines the upper limit of the surface velocity of solifluction. A diagram co rrelating the potential frost creep with the actual surface velocity permit s an inter-site comparison of the relative magnitude of solifluction compon ents. Physically based modelling of periglacial slope evolution requires sy nthetic and more detailed field monitoring and laboratory simulations of so lifluction processes. (C) 2001 Elsevier Science B.V. All rights reserved.